Drive and braking arrangement for a motor vehicle

ABSTRACT

A drive and braking arrangement for a motor vehicle has at least one electric motor which drives the motor vehicle in dependence on the setting of an accelerator pedal. A forward drive or reverse drive selector (15) adjusts the driving direction of rotation of the electric motor, and a sensor is provided for detecting the driving speed of the motor vehicle. In order to control the braking force of a friction brake arrangement acting on at least one wheel of the motor vehicle, an actuating drive is provided which is set to a braking position by an electronic control unit when the accelerator pedal remains in a driving position for longer than a predetermined period of time and at the same time the detected driving speed is zero and/or when the sensor associated with the control unit detects an actual movement of the motor vehicle in the direction opposite to the driving direction selected at the selector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a drive and braking arrangement for a motorvehicle having at least one electric motor which drives the motorvehicle in dependence on the setting of an accelerator pedal, aforward/reverse drive direction selector which adjusts the drivingdirection of rotation of the electric motor or electric motors, meansfor detecting the driving speed of the motor vehicle, and a frictionbrake arrangement acting on at least one wheel of the motor vehicle.

2. Description of the Prior Art

Motor vehicles whose wheels are driven by electric motors, which areknown, for example, from "VDI-Berichte", No. 878, 1991, pages 611 to622, can be prevented from rolling backward on inclined roadways by theelectric motors by means of depressing the accelerator pedal in a mannersimilar to conventional motor vehicles with automatic transmissions.Since the electric motors must be able to apply the driving momentpreventing the motor vehicle from rolling backward in the stationarystate, a comparatively high current passes through the motor which canlead to overheating and destruction of the electric motors.

It is known from DE-A-32 38 196 to prevent motor vehicles with automatictransmission from "creeping" during idling by means of an automaticauxiliary brake. The automatic auxiliary brake has an actuating drivewhich actuates the brake system of the motor vehicle and is set to abraking position when the driving speed lies below a limiting valueclose to zero and the brake pedal and accelerator pedal are notactuated. The auxiliary brake is released when actuating the gas pedaland/or brake pedal.

Further, an auxiliary brake for a motor vehicle with a conventionalmechanical drive train is known from DE 39 09 907 A1. This auxiliarybrake automatically assumes a braking position as soon as the actualrotating direction of the wheel does not correspond to the selecteddrive gear of the gear shift and is automatically released as soon asthe rotating direction of the wheel matches the selected drive gear.This improves comfort as the auxiliary brake is actuated, i.e. appliedor released, automatically without any effort on the part of the driveras soon as the motor vehicle is in a parking or driving situationrequiring the application or release of the auxiliary brake. For thispurpose, the motor vehicle is outfitted with:

an internal combustion engine driving the vehicle via an automatictransmission as a function of the position of the accelerator pedal,

a forward/reverse gear selector,

means for detecting the speed of the vehicle,

an auxiliary brake acting on the wheels of one axle,

an actuating drive for adjusting the braking force of the auxiliarybrake, and

an electronic control unit which actuates the actuating drive in themanner described above.

SUMMARY OF THE INVENTION

In this known vehicle, the actuation of the auxiliary brake does notdepend on the position or setting of the accelerator pedal. Specialmeans for protecting the drive system in the event that the vehicle iskept stationary, i.e. via a motor, by the driving moment of the drivesystem, e.g. on an incline, are not provided, nor are they necessary.

The object of the present invention is to provide a drive and brakingarrangement for a motor vehicle driven by electric motors which not onlyfacilitates operation of the motor vehicle when driving up an incline,but also eliminates the risk of damage to the drive arrangement.

Proceeding from the drive and braking arrangement discussed above, thisobject is met according to the invention in that the friction brakearrangement includes an actuating drive controlling the braking forceand in that an electronic control unit sets the actuating drive to abraking position when the accelerator pedal remains in a drive positionfor longer than a predetermined period of time and at the same time thedetected driving speed is zero and/or when the means associated with thecontrol unit detect an actual movement of the motor vehicle in thedirection opposite the driving direction selected at the selector.

In a drive and braking arrangement of this type, the motor vehicle isautomatically braked in a driving situation which could lead to anoverloading of the electric motors. The actuating drive is set in itsbraking position when the electric motors are stopped by the actuationof the accelerator pedal or produce a moment opposite the direction ofrotation when rolling backward. In either case, operation of the motorvehicle is facilitated.

The brake is released again as a function of the position of theaccelerator pedal. For this purpose, means may be associated with thecontrol unit which detect a driving moment applied by the electric motoror electric motors. The control unit sets the actuating drive to a brakerelease position when the detected driving moment is greater than agiven value. In this way, the brake is only released when the electricmotors have built up a sufficient driving moment.

To make driving up an incline as comfortable and free of jolts aspossible, means are associated with the control unit which, when thevehicle is stationary, determine data representing a holding momentapplied by the electric motor or electric motors in the stationary stateand store the determined moment data in a data storage.

The control unit sets the actuating drive to a brake release positionwhen a torque set by the accelerator pedal exceeds the stored value ofthe holding moment. The current driving moment applied by the electricmotors is also advisably detected in this instance and compared with thestored value.

Finally, in another variant which can prevent the vehicle from rollingbackward when driving on an incline, the control unit sets the actuatingdrive to a brake release position only when the accelerator pedal is setto a driving position and the driving direction set on the drivingdirection selector switch corresponds to the actual movement direction.This variant also ensures that the brake is only released when thedriving moment applied by the electric motor is greater than the brakingmoment.

In order to ensure driving which is as comfortable and free of jolts aspossible, the control unit sets the actuating drive to a brake releaseposition at an actuating speed which changes in accordance with apredetermined characteristic line in a time-dependent manner and/or as afunction of the setting of the accelerator pedal and/or as a function ofa change in the driving speed of the motor vehicle. For example, if theactuating speed of the actuating drive is increased in a continuousmanner when starting to drive, driving can start without jolts and thebrake arrangement is spared at the same time. Excessive dragging of thebrake can be prevented if the actuating speed is increased as deflectionof the accelerator pedal is increased or with increasing driving speed.

The control unit could conceivably always set the actuating drive to theposition of maximum braking moment. Although this type of operationdependably provides for a sufficient braking moment, it shortens thelife of the actuating drive and braking arrangement under certainconditions due to the increased mechanical stress. Therefore, in apreferred construction, means are associated with the control unitwhich, when the vehicle is stationary, detect data representing aholding moment applied by the electric motor or electric motors whenstationary and/or a braking moment adjusted at a manually operateddevice of the friction brake arrangement and store the determined momentdata in a data storage. The control unit then sets the actuating driveto a braking position in which the braking moment of the friction brakearrangement is equal to or greater by a given value than the momentcorresponding to the stored moment data. In this way, only the brakingmoment required for the driving situation in question is adjusted at thebraking arrangement. In addition to the reduced mechanical stress on thebraking arrangement and its actuating drive, this has the advantage thatthe brake can be released faster when starting to drive.

Since not all driving situations allow the braking moment to be detectedand stored when the vehicle is stationary, another advisable variantprovides for the control unit to set the actuating drive to apredetermined braking position in which the braking moment is less thanthe maximum braking moment of the friction brake arrangement. Themechanical stress on the braking arrangement is also comparatively lowin this variant and the brakes can be released faster.

Since the braking action of the braking arrangement can change in atime-dependent manner, it is provided in a preferred construction thatwhen the friction brake arrangement is set to the braking position thecontrol unit sets the friction brake arrangement to a position ofmaximum braking moment when the detected driving speed is greater thanzero in a neutral position of the accelerator pedal. In this way, themaximum braking action is only adjusted when the braking moment provesinadequate in its normal operation setting. This operating mode isparticularly advantageous when the braking arrangement is used at thesame time as a parking brake for the motor vehicle.

The possibility of automatically braking the motor vehicle whenstationary can also be used as an anti-theft function if authorizationchecking means which respond to a password or key are associated withthe control unit and the control unit only sets the actuating drive to abrake release position when authorized. The authorization checking meanscan be a conventional key-actuated lock or a card reader or a keypad forentering a code.

In normal operation of the motor vehicle, the rate of the successivebraking cycles of the type mentioned above is low. On the other hand,the actuating drive must be capable of quickly setting the brakingarrangement to its braking position. Therefore, in order to keep thedrive output of the actuating drive as low as possible an energyaccumulator, particularly a spring accumulator or a fluid pressureaccumulator, is advisably associated with the actuating drive and theactuating drive draws the energy required for setting the brakingposition of the friction brake arrangement from the energy accumulator.For example, the spring accumulator of the actuating drive can be slowlywound up by a comparatively small electric motor. On the other hand, ifthe actuating drive is set to the braking position, the springaccumulator supports the wind-up motor. Moreover, the use of amechanical energy accumulator has the advantage that the brakingarrangement can be set to the braking position by servomechanism supportwhen the ignition is turned off.

The components used for controlling the braking arrangement can beutilized for enhanced protection of the motor vehicle driven by anelectric motor against faulty operation. For this purpose, an advisableconstruction provides a forward/reverse drive direction selector whichadjusts the driving direction of rotation of the electric motor orelectric motors and means which allow the rotating direction of theelectric motor or electric motors to be changed when the selectorsetting is changed only when a stationary state of the vehicle isdetected and/or after the actuating drive has been set to the brakingposition.

The friction brake arrangement mentioned above functions as an auxiliarybrake. This function can be achieved in that the actuating driveadditionally acts on the foot brake or operating brake of the motorvehicle which can be actuated by a brake pedal. However, forsafety-related reasons, it can also serve as an additional brakingarrangement which can be actuated manually as well as by the actuatingdrive. To keep construction costs as low as possible, each electricmotor is combined in its own constructional unit with wheel brakes ofthe driven wheels in an embodiment in which the electric motors driveseparate wheels of the motor vehicle.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in detail in the following with reference tothe drawing. The drawing shows a block diagram of a drive and brakingarrangement, according to the invention, for a motor vehicle withfour-wheel drive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The motor vehicle has an internal combustion engine 1 with a generatorarrangement 3 which is attached thereto by flanges and supplies electricmotors 7 at the individual wheels 9 via an electronic control unit 5.The control unit 5 controls the output of the internal combustion engine1 via actuating drives, not shown in more detail, and the electricalpower supplied to the electric motors 7 by the generator arrangement 3as a function of the position of the accelerator pedal 11, whoseposition is determined by a position sensor 13. The rotating directionof the electric motors 7, and accordingly the driving direction of themotor vehicle, is determined by a manually operated selector 15 by meansof which the driver can shift between forward and reverse drivingdirections. The driver determines the torque generated by the electricmotors 7 at the individual wheels 9 and/or the speed of the electricmotors 7 via the accelerator pedal 11.

Each electric motor 7 forms a constructional unit with wheel brakedevices 17 of an operating brake arrangement, not shown in detail, ofthe motor vehicle which can be actuated via a brake pedal. Aconventional auxiliary brake arrangement acts additionally on a portionof the wheel brake arrangements 17, the rear wheels 9 in this instance,and has a manually actuated hand brake lever 19 that is connected withthe wheel brake arrangements 17 of these wheels 9 via a mechanical orhydraulic force transmission arrangement 21. The auxiliary brakearrangement can act on the wheel brake arrangements 17 of the operatingbrake or on separate wheel brake arrangements.

A motor vehicle of the type described above could also be heldstationary on an incline and prevented from rolling backward byactuating the accelerator pedal 11 without actuating the operating brakeor the auxiliary brake. The holding moment produced in the stationarystate of the electric motors 7 generates considerable heat in theelectric motors 7 and, under certain conditions, leads to theirdestruction. To relieve the electric motors 7 in the stationary statefrom the holding moment, actuating drives 23 are associated with thewheel brake arrangements 17 of either the operating brake or theauxiliary brake. These actuating drives 23 are controlled by a brakecontrol unit 25. The brake control unit 25 responds to information fromsensors 27 arranged at the electric motors 7 or at the wheels 9 drivenby the electric motors 7. This information supplies data concerning thenumber of revolutions of the wheels 9 and accordingly the driving speedand/or data concerning the drive torque applied by the electric motors7. The torque data can be calculated in particular from the electricalpower consumed by the electric motors 7 so that these data can also besupplied, if necessary, by the control unit 5. The brake control unit 25detects the holding moment applied by the electric motors 7 at a drivingspeed of zero and adjusts the actuating drives 23 to a braking momentwhich corresponds to the holding moment of the electric motors 7 orwhich, for safety reasons, exceeds this holding moment by a givenamount. However, the actuating drives 23 are only set to their brakingposition when the accelerator pedal 11 has been depressed for longerthan a given period of time, e.g. one second, and when the stationarystate of the vehicle is sustained at the same time. The data of the lastdetected holding moment of the electric motors 7 are stored in a datastorage 29, whereupon the electric motors 7 are turned off regardless ofthe actuated accelerator pedal 11.

In order to continue driving, the accelerator pedal 11 must be depressedbeyond the last adjusted position and a torque exceeding the valuestored in the data storage 29 must be built up at the electric motors 7.The brake control unit 25 sets the actuating drives 23 to a brakerelease position as soon as the driving moment applied by the electricmotors 7 exceeds the stored value of the braking moment. However, thebrake is released in accordance with a predetermined time function withthe result that the motor vehicle can be set in motion only gradually atfirst. This allows the brake control unit 25 to compare speedinformation supplied by the sensors 27, which also contains informationon the current rotating direction of the electric motors and accordinglyinformation on the current movement direction of the motor vehicle, withinformation concerning the driving direction adjusted at the selector15. The brake control unit 25 continues to release the brake only whenthe current movement direction conforms to the selected drivingdirection. If the current movement direction does not match the selecteddriving direction, the actuating drives 23 are set in the direction ofincreased braking force again. The vehicle is accordingly prevented fromrolling backward on an incline.

The speed at which the brake control unit 25 sets the actuating drives23 to the brake release position can depend on a predeterminedtime-dependent characteristic line and beyond this or alternatively canalso be controlled in proportion to the actuating speed of theaccelerator pedal 11. The preselected brake release speed can increasecomfort and eliminate jolting when driving is resumed.

In contrast to conventional motor vehicles with wheels driven viamechanical transmission, the motor vehicle described above which isdriven by electric motors must be secured against unintentional rollingvia the auxiliary brake when parking. The brake control device 25 allowsan automatic parking safety operation and sets the actuating drives 23to a braking position when the sensors 27 determine that the vehicle isstationary at the same time that the position sensor 13 detects that theaccelerator pedal 11 is located in its unactuated neutral position andan ignition lock indicated at 31 in the drawing is set to the parkingposition. In this case also, the brake control unit 25 sets theactuating drives 23 to a position in which the braking moment is equalto the last holding moment applied by the electric motors 7, but atleast equal to a predetermined braking moment. The selected brakingmoment is advisably less than the maximum braking moment of the brakingarrangements, but still ensures a dependable holding of the motorvehicle under normal operating conditions. Selecting the braking momentvalue below the maximum braking moment shortens the brake release timeand spares the braking arrangement. However, if the brake control unit25 subsequently determines after setting the actuating drives 23 thatthe motor vehicle has begun to roll again, the actuating drives 23 areset to the maximum braking moment. When driving is resumed, theactuating drive is only set fully to the brake release position againwhen the driving moment applied by the electric motors 7 after actuatingthe accelerator pedal 11 exceeds the value of the braking moment storedin the data storage 29 and the actual movement direction of the motorvehicle conforms to the driving direction set at the selectorarrangement 15. The brake release speed can also be controlled as afunction of time or as a function of the accelerator pedal position inthis instance.

The ignition lock 31 or an authorization checking device 33 associatedwith the ignition lock 31, e.g. a code card reader or a code entrykeypad, can be used to prevent theft of the motor vehicle in that theactuating drives 23 which are set to the brake position for parking areonly set to the brake release position by the brake control unit 25 whenthe ignition key fitting the ignition lock 31 is used or when thecorrect password information is entered in the authorization checkingdevice 33.

Each actuating drive 23 includes an energy accumulator 35, e.g. a springaccumulator, which is wound up by an electric motor of the actuatingdrive 23, not shown in detail, when releasing the brake or betweensuccessive braking cycles and either delivers all the power to beapplied by the actuating drive 23 for actuating the wheel brakearrangements 17 or supports the actuating drive 23 in this respect.

In order to rule out faulty operation of the driving direction selector15, e.g. an unintentional change of direction, the control unit 5 allowsthe rotating direction of the electric motors 7 to be changed only whenthe brake control unit 25 detects a vehicle speed of zero and/or whenthe actuating drives 23 have been set for a short time to a brakingposition applying the holding moment. Obviously, for reasons of safety,the actuating drives 23 cannot be actuated by the brake control unit 25at vehicle speeds greater than zero. Rather, the auxiliary brake onlyresponds to the manual actuation of the hand brake lever 19.

In the embodiment of the invention described above, the wheel brakearrangements 17 are provided with separate actuating drives 23 which areindependent of the manually actuated components of the auxiliary brakeso that the auxiliary brake can still be actuated manually in the eventof failure of the electronic equipment or power supply or actuatingdrives 23. However, if necessary, a common actuating drive can beassociated with a plurality of wheel brake arrangements 17 and can alsoact on the wheel brake arrangements 17 via the force transmission means21 when so designed. The actuating drives 23 can also be used toreinforce the operating brake if desired, e.g. if the braking power ofthe operating brake is reduced due to wear or overheating.

We claim: IN THE CLAIMS:
 1. A drive and braking arrangement for a motorvehicle, comprising: an accelerator pedal having a plurality ofpositions; at least one electric motor provided so as to drive the motorvehicle in dependence on the position of the accelerator pedal; aforward/reverse selector provided so as to adjust a driving direction ofrotation of the at least one motor; means for detecting the drivingspeed of the motor vehicle; a friction brake arrangement provided so asto act with a braking force on at least one wheel of the motor vehicle;actuating drive means for controlling the braking force of the frictionbrake arrangement; and electronic control means for setting theactuating drive means to a braking position when the detecting meansdetects an actual movement of the motor vehicle in a direction oppositeto the driving direction selected at the selector, the detecting meansbeing associated with the control means, the control means also settingthe actuating drive means to a braking position when the acceleratorpedal remains in a driving position for longer than a predeterminedperiod of time and at the same time the detected driving speed is zero.2. An arrangement according to claim 1, and further comprising meansassociated with the control means for detecting a driving moment appliedby the at least one electric motor, the control means setting theactuating drive means to a brake release position when the detecteddriving moment is greater than a given value.
 3. An arrangementaccording to claim 1, and further comprising means associated with thecontrol means for determining data representing a holding moment appliedby the at least one electric motor when the vehicle is stationary, andfor storing the determined moment data in a data storage, the controlmeans setting the actuating drive means to a brake release position whena torque set by the accelerator pedal exceeds the stored value of theholding moment.
 4. An arrangement according to claim 1, wherein tirecontrol means sets the actuating drive means to a brake release positiononly when the accelerator pedal is set in a driving position and theselected driving direction corresponds to the actual movement direction.5. An arrangement according to claim 1, wherein the control means setsthe actuating drive means to a brake release position at least one of atan actuating speed which changes in accordance with a predeterminedcharacteristic line in a time-dependent manner, as a function of thesetting of the accelerator pedal and as a function of a change in thedriving speed of the motor vehicle.
 6. An arrangement according to claim1, wherein the friction brake arrangement includes a manually operabledevice, and further comprising means associated with the control meansfor determining data representing at least one of a holding momentapplied by the at least one electric motor when the vehicle isstationary and a braking moment adjusted at the manually operable deviceof the friction brake arrangement, and for storing the determined momentdata in a data storage, the control means setting the actuating drivemeans to a braking position in which a braking moment of the frictionbrake is at least equal to the stored moment data.
 7. An arrangementaccording to claim 6, wherein the control means sets the actuating drivemeans to a braking position in which the braking moment of the frictionbrake arrangement is greater than to the stored moment data by apredetermined value.
 8. An arrangement according to claim 1, wherein thefriction brake arrangement has a braking moment, the control meanssetting the actuating drive means to a predetermined braking position inwhich the braking moment is less than a maximum braking moment of thefriction brake arrangement.
 9. An arrangement according to claim 6,wherein, when the friction brake arrangement is set to the brakingposition, the control means sets the friction brake arrangement to aposition of maximum braking moment when the detected driving speed isgreater than zero in a neutral position of the accelerator pedal.
 10. Anarrangement according to claim 1, and further comprising authorizationchecking means, which respond to one of a password and a key, associatedwith the control means so that the control means only sets the actuatingdrive means to a brake release position when authorized.
 11. Anarrangement according to claim 1, and further comprising an energyaccumulator associated with the actuating drive means so that theactuating drive means draws energy required for setting the brakingposition of the friction brake arrangement from the energy accumulator.12. An arrangement according to claim 11, wherein the energy accumulatoris a spring accumulator.
 13. An arrangement according to claim 11,wherein the energy accumulator is a fluid pressure accumulator.
 14. Anarrangement according to claim 1, wherein the forward/reverse drivedirection selector adjusts the driving direction of rotation of the atleast one electric motor, the electronic control means permitting therotating direction of the at least electric motor to be changed when asetting of the selector is changed only when at least one of astationary state of the vehicle is detected and after the actuatingdrive means has been set to the braking position.
 15. An arrangementaccording to claim 1, wherein each electric motor drives a separatewheel of the motor vehicle and is combined in a constructional unit withthe friction brake arrangement of the respective wheel.